Surface dynamics of the integral membrane protein bacteriorhodopsin

Recently, there has been great interest in determining the three-dimensional structures of membrane proteins, particularly bacteriorhodopsin, for which a variety of possible folding arrangements have been suggested. In this paper we present nuclear magnetic resonance (NMR) spectra of deuterated bacteriorhodopsin, and use the data to help interpret the various suggested bacteriorhodopsin folding patterns. The results strongly indicate that (1) a membrane surface (+/- 1 residue) may be defined by NMR in bacteriorhodopsin; (2) all amino acids inside the surface are essentially crystalline; (3) all amino acids outside the surface (surface residues) in bacteriorhodopsin are highly mobile on the time scale of the 2H NMR experiments; (4) NMR data may be used to help evaluate the various structural models that have been proposed; (5) aggregation of purple membrane sheets may lead to an immobilization of the surface residues.